This invention relates to aeration panels for injecting fine bubbles of air into liquid contained in a tank or basin to diffuse oxygen into the liquid.
The patent to Messner, U.S. Pat. No. 4,624,781, discloses a panel-type air diffusion device for injecting small air bubbles into a body of water. That device has a flexible membrane which is clamped to a support plate around its periphery and includes hold-down strips clamping the membrane to the support plate in the central region to prevent billowing of the membrane. In addition, ballast weights may be included to prevent the diffusion device from floating upwardly in the body of water. In this Messner patent, the membrane is clamped directly between the support plate and the peripheral hold-down strips, and the ends of the middle hold-down strips are spaced from the peripheral hold-down strips to permit passage of air from a central inlet beneath the membrane to the outer portions of the diffuser.
As noted in the later Messner U.S. Pat. No. 5,015,421, the connection between the peripheral clamping strips and the membrane of the diffuser in U.S. Pat. No. 4,624,781 tends to weaken in the regions of the screw or rivet attachment points holding the edge strips and, to overcome that problem, U.S. Pat. No. 5,015,421 discloses a membrane which is clamped to a support panel around its periphery with special continuous clamping arrangements rather than point attachments such as screws or rivets. That patent also discloses middle hold-down strips which extend only along a portion of the panel, leaving unrestrained parts of the membrane near the ends of the panel.
German Offenlegungsschrift No. 29 42 607 of Messner describes an aeration panel having a perforated foil and an unperforated foil which are supported and clamped around their periphery by bolts with a layer of adhesive interposed between the two foil layers at the periphery. European Patent Publication No. 0 229 386 describes a disk-shaped aerator having a rubber membrane bonded to a support disk around its periphery. None of these prior art arrangements, however, have been completely satisfactory from the standpoint of retaining the peripheral edge of a membrane in a submerged aerator in secure sealing relation with a support plate and restraining central regions of the membrane from billowing upwardly while permitting air to pass from a central inlet to all regions of the aerator.